The invention relates to an electronic valve actuator of a hydraulic system. The invention relates particularly to regulating an electronic valve actuator through load dependence and pressure compensation.
A hydraulic actuator or cylinder is well known in the art and is used to give unidirectional force through a unidirectional stroke. Hydraulic actuators have many applications such as construction equipment, manufacturing machinery and civil engineering.
Hydraulic actuators get their power from pressurized hydraulic fluid. The flow of hydraulic fluid to and from the actuator is controlled by a valve. Depending upon the application, hydraulic actuators are faced with loads that vary greatly. In these situations, the requirements which need to be accounted for by the actuator conflict with the requirements that need to be accounted for in the valve. For example, with light loads, the valve area needs to be large to allow for high actuator speeds. When the loads are large, the valve area needs to be quite small to prevent excessive actuator speeds.
Typically, the valve opening area is proportionally commanded by the operator's input. For example, a 0-100% joystick command results in a 0-100% valve opening area. This can result in poor resolution. When actuator velocity is 0-100%, poor resolution occurs when the valve opening area is 0-10% and the joystick command is also limited from 0-10%.
One method to address this issue is to use a hydraulic compensator that regulates pressure drop across the control orifice area of the valve to a relatively constant pressure drop. A problem with this approach is that when the maximum valve area needs to be oversized for a light load condition, the compensator adds additional pressure drop even when fully open, reducing the maximum lowering velocity of the light load.
To avoid unsafe lowering velocities with high loads, a flow limiting valve may be used, but this still carries the issue of poor resolution when lowering high loads (e.g. a 10% joystick command can result in 100% actuator velocity).
Safety issues are particularly present when actuators are used with a forklift hoist. The lowering function for a forklift hoist usually works by gravity of the fork whether loaded or not. Without pressure compensation, the larger the load the higher the acceleration would be. This causes an unsafe operating condition for an operator.